Insights into the degradation mechanisms and pathways of cephalexin during homogeneous and heterogeneous photo-Fenton processes.

The widespread occurrence of antibiotics in the environment poses a potential threat to human health. The photo-Fenton process has demonstrated better degradation performance compared with the conventional wastewater treatment processes. In this study, the degradation of cephalexin was evaluated comparatively by homogeneous (Fe2+/H2O2/UV) and heterogeneous (MoS2@Fe/H2O2/UV) photo-Fenton processes. Key influencing factors affecting photo-Fenton performance were assessed, confirming the optimum Fe2+ concentration at 0.2016 mg L-1 and H2O2/Fe2+ molar ratio at 6. Higher degradation efficiency (73.10%) and pseudo-first-order degradation rate constant (0.0078 min-1) were achieved with the assistance of MoS2@Fe as the heterogeneous catalyst. Completely different degradation products were identified in the homogeneous and heterogeneous photo-Fenton processes, with main degradation pathways proposed as ß-lactam ring-opening, sulfoxide formation, demethylation, N-dealkylation, decarbonylation, hydroxylation and deamination in the Fe2+/H2O2/UV system and ß-lactam ring-opening, hydroxylation, dehydration, amide hydrolysis, and demethylation and ring contraction in the MoS2@Fe/H2O2/UV system, respectively. The formation of newly identified products might root in the attack on cephalexin from active species (i.e., OH, h+, e-, O2-) photoinduced by the MoS2@Fe catalyst. Results also indicated the importance of understanding the underlying mechanisms and pathways to eliminate the antimicrobial activities of antibiotics in the future.

Degradation of fluoroquinolones in homogeneous and heterogeneous photo-Fenton processes: A review.

Fluoroquinolone antibiotics are frequently detected in the environment causing potential hazards to ecological and human health. Inadequate removal efficiencies were reported for fluoroquinolones during conventional wastewater treatment processes whereas the application of photo-Fenton reactions has attracted much attention due to their high reaction rate. This article summarizes the recent proceedings on homogeneous and heterogeneous photo-Fenton degradation of fluoroquinolones. Degradation efficiencies of fluoroquinolones were discussed as well as rate constants for a distinct comparison. The influences of initial fluoroquinolone concentration, H2O2, Fe2+, pH and temperature were also investigated on homogeneous photo-Fenton degradation of fluoroquinolones. The currently applied heterogenous catalysts were considered including iron oxides catalysts, iron-based composite catalysts and iron-based semiconductor. In addition, the degradation pathways for typical fluoroquinolones were proposed with the products identified in the literature. The results indicated the better performance with the aid of heterogeneous catalysts due to the generation of more active species. Intermediate products at smaller molecular weight were obtained through various types of pathways under heterogeneous photo-Fenton degradation of fluoroquinolones, implying a practical application with biological treatment processes for fully mineralization.